when you are recording, make sure you set the volume of the motif on high (but below the peak). use the monitoring meter to ensure that you won't have to boost the volume after it's already recorded. if you boost the volume after you record, you're boosting everything else in that recording, including white noise.
it could be an impedance level that's off
it could be the grounding. try plugging the renn into a different outlet from the motif (not sure if the renn has 3 prongs, i own a mpc studio

)
it could be a damaged 1/4'' wire. try replacing the wire (don't necessarily have to be gold plated)
cheap wires do suck
or you can try a HUM eliminator (around 70$).. which definitely works.
this might help clear up some stuff:
http://www.alectrosystems.com/tips/audio_tips/audio_tip_LowZ.htm